Feat: support more functions (transform fns)

Closes #25 (closed)

Fns to support

• round
• abs
• absent
• ceil
• changes
• delta
• exp
• floor
• sort
• sort_desc
• sqrt
• vector

Todo

• add integration tests

src/query/fns/mod.rs

@@ -19,7 +19,6 @@ pub mod aggregate;
 #[cfg(feature = "metricsql")]
 pub mod label;
 pub mod rollup;
-#[cfg(feature = "metricsql")]
 pub mod transform;
 
 // This macro takes a name and formatting arguments which are directly passed to the `write` macro